In industrial measuring and automation technology, in connection with the control of automated filling processes of flowable media, such as, for instance, powder, granular material, liquids or pastes, filling machines embodied as line fillers or rotary fillers are applied, such as illustrated, for example, in CA 2,023,652, DE A 10 2006 031969, EPA 893 396, EP A 405 402, U.S. Pat. Nos. 7,114,535, 6,474,368, 6,026,867, 5,975,159, 5,865,225, 5,595,221, 4,588,001, 4,532,968, 4,522,238, 4,053,003, 3,826,293, 3,519,108, US A 2006/0146689, US A 2003/0037514, WO A 08/034,710, WO07/048,742, or WO A 04/049641. In such filling machines, the containers, for example, bottles, ampoules, cups, glasses, cans or the like, which are to be filled with a charge of the respective medium, such as, for instance, a pasty or doughy food, a solvent, a lacquer or a paint, a cleaning agent, a drink, a medicine or the like, are supplied one after the other via a corresponding feed system to the filling machine. The actual filling procedure occurs during a period of time in which the particular container is located within a filling location installed on the filling machine below a filling tip dispensing the medium. Following the filling with an, as much as possible, highly precisely metered charge of the medium, the containers leave the filling machine and are automatically conveyed further. Typical throughput rates of such filling machines can lie quite well in the order of magnitude of 20,000 containers per hour.
For precisely ascertaining the volume of medium actually metered in each case, often applied in filling machines are in line measuring devices, which highly accurately ascertain the charge to be metered during the corresponding filling procedure by means of directly measured and internally totalized flow rates of the medium, as it is allowed to flow through a measuring transducer of the measuring device serving for physical-to-electrical transducing of the measured variable to be registered. These in line measuring devices then output, especially in real time, in the form of a primary measured value of the measuring device, especially a primary measured value formatted corresponding to the requirements of the bottling process, for example, to a superordinated programmable logic controller (PLC), in order so to enable a correspondingly exact, as were it, also fast and robust control of the bottling process, which is, most often, operated in batch mode. The measuring transducer is, for such purpose, correspondingly connected via in- and outlet side, most often standardized, connection elements, for example, screw connections or flanges, to a line segment supplying medium to be measured, or a line segment removing a measured medium, of a pipeline system of the filling plant conveying the medium during operation. In case required, there serve, besides the usually rigidly formed line segments, additionally extra holding apparatuses for affixing the measuring device within the filling machine.
The actual filling procedure and, associated therewith, the actual measuring cycle, in which medium to be measured flows through the measuring transducer, can last, in the case of filling processes run in batch operation, from a few seconds down to greatly less than a second. Preceding the measuring cycle wherein the charge is filled, and, accordingly, also following such, the measuring transducer resides in a ready state, during which no medium flows through the measuring transducer, and, thus, no medium is metered.
Because of their very high accuracy of measurement, even in the case of comparatively strongly fluctuating flow rates, especially also in filling processes operated discontinuously and/or in batch operation, as well as also a comparatively good reproducibility of the measured values delivered under such conditions, in spite of this, very near in time, such as, for example, also explained in the Durchflusss Handbuch (Flow Handbook), 4th edition 2003, ISBN 3-9520220-3-9 in the section “Abfuell- and Dosieranwendungen (Filling and Metering, or Dosing, Applications”, page 213 ff., as well as in the patent literature, U.S. Pat. Nos. 7,302,356, 5,975,747, WO A 00/057325 or WO A 08/034,710, in line measuring devices, especially in line measuring devices embodied as Coriolis mass flow measuring devices, are applied, which, by means of a measuring transducer of vibration-type and a thereto connected, measuring device electronics, accommodated most often in a separate electronics housing, induce in the flowing medium reaction forces, for example, Coriolis forces, accelerating forces, frictional forces or the like, and, derived from these, produce at least one measurement signal correspondingly representing the at least one measured variable, for example, a mass flow, a density, a viscosity or another process parameter. Construction and operation of flow rate measuring, in line devices of the type being discussed, equipped with a measuring transducer of vibration-type are, moreover, sufficiently known to those skilled in the art. Examples of such in line measuring devices, especially also in line measuring devices embodied as Coriolis mass flow measuring devices, equipped with a measuring transducer of vibration-type or, however, also individual components thereof, such as, for instance, the measuring transducer, as well as also their special application, are described at length and in detail, besides in the already mentioned state of the art, in, among others, WO A 99/40 394, WO A 99/39164, WO A 98/07009, WO A 95/16897, WO A 88/03261, WO A 08/059,015, WO A 08/013,545, WO A 08/011,587, WO A 07/005,024, WO A 06/127527, WO A 06/104690, WO A 06/062856, WO A 05/093381, WO A 05/031285, WO A 05/003690, WO A 03/095950, WO A 03/095949, WO A 02/37063, WO A 01/33174, WO A 01/02 816, WO A 00/57141, WO A 00/14 485, U.S. Pat. Nos. 7,392,709, 7,360,451, 7,343,253, 7,340,964, 7,299,699, 7,296,484, 7,213,470, 7,213,469, 7,181,982, 7,080,564, 7,077,014, 7,073,396, B 7,040,180, 7,040,181, 7,040,179, 7,017,424, 6,920,798, 6,910,366, 6,895,826, 6,883,387, 6,880,410, 6,860,158, 6,840,109, 6,810,719, 6,805,012, 6,758,102, 6,705,172, 6,691,583, 6,666,098, 6,651,513, 6,564,619, 6,557,422, 6,519,828, 6,516,674, 6,513,393, 6,505,519, 6,471,487, 6,397,685, 6,330,832, 6,318,156, 6,311,136, 6,223,605, 6,168,069, 7,337,676, 6,092,429, 6,073,495, 6,047,457, 6,041,665, 6,006,609, 5,979,246, 5,945,609, 5,926,096, 5,869,770, 5,861,561, 5,796,012, 5,796,011, 5,796,010, 5,731,527, 5,691,485, 5,648,616, 5,616,868, 5,610,342, 5,602,346, 5,602,345, 5,531,126, 5,476,013, 5,429,002, 5,398,554, 5,359,881, 5,301,557, 5,291,792, 5,287,754, 5,253,533, 5,218,873, 5,095,761, 5,069,074, 5,050,439, 5,044,207, 5,027,662, 5,009,109, 4,962,671, 4,957,005, 4,911,006, 4,895,031, 4,876,898, 4,852,410, 4,823,614, 4,801,897, 4,777,833, 4,738,144, 4,733,569, 4,660,421, 4,491,025, 4,187,721, US A 2008/0190195, US A 2008/0189079, US A 2008/0189067, US A 2008/0141789, US A 2008/0092667, US A 2008/0047361, US A 2008/0011101, US A 2007/0186685, US A 2007/0151371, US A 2007/0151370, US A 2007/0144234, US A 2007/0119265, US A 2007/0119264, US A 2006/0201260, US A 2005/0139015, US A 2003/0208325, US A 2003/0131668 or the assignee's own, not pre-published DE102007062397.
Each of the therein illustrated measuring transducer comprises at least one, essentially straight, or at least one curved, measuring tube for conveying the, in given cases, extremely viscous or, however, also rather low viscosity, medium. In operation of the in line measuring device, the at least one measuring tube is caused to vibrate during operation, for the purpose of generating oscillation forms influenced by, among other things, the through flowing medium, especially its instantaneous mass flow. As excited oscillation form—the so-called wanted mode—in the case of measuring transducers with curved, e.g. U-, V- or Ω-shaped, measuring tube, usually that eigenoscillation form is selected, in the case of which the measuring tube executes bending oscillations about an imaginary bending oscillation axis of the measuring transducer extending essentially parallel to an imaginary longitudinal axis of the measuring transducer imaginarily connecting an inlet end of the measuring tube with an outlet end of the measuring tube or coinciding with such, so that it executes bending oscillations—in the manner of a kind of end clamped cantilever—in the form of pendulum-like movements essentially mirror symmetrically (in the following shortened to “symmetrically”) about an imaginary central plane of the measuring tube at a lowest natural resonance frequency. In the case of measuring transducers with straight measuring tube, in contrast, for the purpose of producing mass flow dependent oscillation forms, often such a wanted mode is selected, wherein the measuring tube executes bending oscillations at least partially symmetrically about its aforementioned central plane, essentially in a single imaginary plane of oscillation, for instance, in the manner of a beam, or string, clamped on both ends. The imaginary central plane corresponds in both cases most often to that symmetry plane of the measuring tube, in given circumstances, also of the total measuring transducer, in which the cross section extending through the center of such measuring tube lies, and which symmetry plane is, thus, coplanar with this cross section.
As a result of such, for example, pendulum- or string-like, bending oscillations, as is known, Coriolis forces dependent on the mass flow, or the mass flow rate, are induced in the through flowing medium. These Coriolis forces, in turn, lead to the superimposing on the excited oscillations of the wanted mode, in the case of curved measuring tubes, thus, pendulum-like cantilever oscillations, thereto equal-frequency, bending oscillations of at least one likewise natural, second oscillation form, the so-called Coriolis mode. In the case of measuring transducers with curved measuring tube, these cantilever oscillations in the Coriolis mode driven by Coriolis forces correspond usually to that eigenoscillation form, in the case of which the measuring tube executes also rotary oscillations about an imaginary vertical axis directed essentially perpendicularly to the longitudinal axis. In the case of measuring transducers with straight measuring tube, in contrast, the oscillations in the Coriolis mode are formed, coplanarly with the wanted mode oscillations, as bending oscillations of equal oscillation frequency. For the mentioned case, in which oscillations serve as wanted mode, which are essentially symmetric with respect to the aforementioned central plane of the respective measuring tube, the oscillations of the measuring tube in the Coriolis mode are formed essentially anti- or point-symmetrically (in the following shortened to “antisymmetrically”) with respect to the central plane of the measuring tube. Straight measuring tubes can, such as, for example, shown in U.S. Pat. Nos. 6,006,609 or 7,017,424, additionally also be excited to torsional oscillations about an imaginary longitudinal axis of the measuring tube, or the measuring transducer.
For exciting oscillations of the at least one measuring tube, measuring transducers of vibration-type have, additionally, an exciter mechanism driven, during operation, by an electrical exciter signal, e.g. in the form of a controlled electrical current, generated and correspondingly conditioned by a driver circuit of an associated measuring device electronics. The exciter mechanism excites the measuring tube to bending oscillations in the wanted mode by means of at least one electrical current driven, and, thus, electromechanical, especially electrodynamic, oscillation exciter acting, during operation, essentially directly on the measuring tube. Furthermore, such measuring transducers include a sensor arrangement with, especially electrodynamic, oscillation sensors for at least pointwise registering of inlet-side and outlet-side oscillations of the at least one measuring tube, especially the oscillations in the Coriolis mode, and for producing electrical sensor, or also oscillation measurement, signals serving, in each case, as a measurement signal of the measuring transducer influenced by the process parameter to be registered, such as, for instance, mass flow or density.
Due to the superpositioning of wanted and Coriolis modes, the oscillations of the vibrating measuring tube registered by means of the sensor arrangement on the inlet side and on the outlet side have a measurable phase difference also dependent on the mass flow. Usually, the measuring tubes of such measuring transducers, e.g. as applied in Coriolis mass flow meters and trimmed most often also to high oscillatory quality factors of far greater than 100, especially to 5000 or thereover, are excited, during operation, to an instantaneous natural resonance frequency of the oscillation form selected for the wanted mode, especially at an oscillation amplitude controlled to be constant and/or matched to the medium. Since this resonance frequency depends, especially, also on the instantaneous density of the medium, market-usual Coriolis mass flow meters can measure, besides the mass flow, supplementally, also the density of flowing media. Additionally, it is also possible, such as, for example, shown in U.S. Pat. Nos. 6,651,513, 6,910,366 or 7,080,564, directly to measure, by means of measuring transducers of vibration-type, viscosity of the medium flowing through such a measuring transducer, for instance, based on an excitation power required for exciting the oscillations. The excitation power can, in turn, be ascertained, for example, on the basis of the exciter, or driver, signal delivered by the driver circuit, or, such as, among others, mentioned in U.S. Pat. No. 6,910,366, on the basis of the operating parameters for the driver circuit controlling the generating of the driver signal. In the case of at least one, at least sectionally straight, measuring tube, viscosity can also be determined based on torsional oscillations of the same.
In the case of measuring transducers with two measuring tubes, these are most often connected into the process line (most often embodied as a rigid pipeline) via a distributor piece extending on the inlet side between the measuring tubes and an inlet-side connecting flange as well as via a distributor piece extending on the outlet side between the measuring tubes and an outlet-side connecting flange. In the case of measuring transducers with a single measuring tube, the latter communicates most often with the process line via an essentially straight, connecting tube piece on the inlet side as well as via an essentially straight connecting tube piece on the outlet side. Additionally, each of the shown measuring transducers with a single measuring tube includes at least one, for example, tube-, box- or plate-shaped, counteroscillator embodied as one piece or a plurality of parts coupled on the inlet side to the measuring tube to form a first coupling zone and coupled on the outlet side to the measuring tube to form a second coupling zone, and, during operation, essentially at rest or oscillating opposite-equally to the measuring tube, thus with equal frequency and opposite phase. The inner part of the measuring transducer formed by means of measuring tube and counteroscillator is most often held, alone, by means of the two connecting tube pieces (via which the measuring tube communicates, during operation, with the process line), in a protective measuring transducer housing, especially in a manner enabling oscillations of the inner part relative to the housing. In the case of the measuring transducers with a single, essentially straight measuring tube illustrated, for example, in U.S. Pat. Nos. 5,291,792, 5,796,010, 5,945,609, 7,077,014, US A 2007/0119264, WO 0,102,816 or also WO 9,940,394, the measuring tube and the counteroscillator are, such as quite usual in the case of conventional measuring transducers, oriented essentially coaxially relative to one another. In the case of usually marketed measuring transducers of the aforementioned type, most often also the counteroscillator is embodied essentially tubularly in the form of an essentially straight, hollow cylinder, which is so arranged in the measuring transducer, that the measuring tube is jacketed at least partially by the counteroscillator. Most often used as materials for such counteroscillator, especially also in the case of application of titanium, tantalum or zirconium for the measuring tube, are comparatively cost effective, steel types, such as, for instance, structural steel or free-machining steel.
The exciter mechanism of measuring transducers of the type being discussed includes usually at least one electrodynamic oscillation exciter and/or an oscillation exciter acting differentially on the at least one measuring tube and the, in given circumstances, present counteroscillator or the, in other given circumstances, present, other measuring tube, while the sensor arrangement includes an inlet-side, most often likewise electrodynamic, oscillation sensor as well as at least one, thereto essentially equally constructed, outlet-side oscillation sensor. Such electrodynamic and/or differential, oscillation exciters of usually marketed measuring transducers of vibration-type are formed by means of a magnet coil, through which electrical current flows, at least at times. In the case of measuring transducers having a measuring tube and a counteroscillator coupled therewith, most often the magnet coil is affixed on the latter. Such electrodynamic and/or differential oscillation exciters additionally include, interacting with the at least one magnet coil, especially plunging into it, serving as armature, a rather elongated, especially rod-shaped, permanent magnet, which is affixed correspondingly to the measuring tube to be moved. The permanent magnet and the magnet coil serving as exciter coil are, in such case, usually so oriented, that they extend essentially coaxially relative to one another. Additionally, in the case of conventional measuring transducers, the exciter mechanism is usually embodied and placed in the measuring transducer in such a manner, that it acts essentially centrally on the at least one measuring tube. In such case, the oscillation exciter and, insofar, the exciter mechanism, such as, for example, also proposed in the case of the measuring transducers disclosed in U.S. Pat. Nos. 5,796,010, 6,840,109, 7,077,014 or 7,017,424, is most often affixed outwardly on the measuring tube at least pointwise along an imaginary central peripheral line of the measuring tube. Alternatively to an exciter mechanism formed by means of oscillation exciters acting rather centrally and directly on the measuring tube, it is possible, such as, among other things, provided in U.S. Pat. Nos. 6,557,422, 6,092,429 or 4,823,614, to use, for example, exciter mechanisms formed by means of two oscillation exciters affixed not at the center of the measuring tube, but, instead on the in- and outlet sides thereof, or, such as, among other things, provided in U.S. Pat. Nos. 6,223,605 or 5,531,126, for example, also by means of an exciter mechanism formed by an oscillation exciter acting between the, in given circumstances, present counteroscillator and the measuring transducer housing.
In the case of most market-ordinary measuring transducers of vibration-type, the oscillation sensors of the sensor arrangement are, such as already indicated, essentially of equal construction to that of the at least one oscillation exciter, at least to the extent that they work according to the same principle of action. Accordingly, also the oscillation sensors of such a sensor arrangement are most often in each case formed by means of: At least one magnet coil—usually affixed to the, in given circumstances, present counteroscillator —, at least at times, passed through by a variable magnetic field, and, associated therewith, containing, at least at times, an induced measurement voltage; as well as, affixed to the measuring tube and interacting with the at least one magnet coil, a rod-shaped permanent magnet, which delivers the magnetic field. Each of the aforementioned coils is additionally connected by means of at least one pair of electrical connecting lines with the mentioned measuring device electronics of the in line measuring device. These lines are, most often, led on shortest possible paths from the coils over the counteroscillator to the transducer housing.
The measuring device electronics (often also referred to as measurement transmitter, or, simply, transmitter) of conventional in line measuring devices of the aforementioned type most often contain a microcomputer, which delivers digital measured values in real time and which is formed, for example, by means of a digital signal processor. This includes, besides at least one corresponding processor and its associated peripheral circuit components, such as e.g. A/D converters and D/A converters, most often also corresponding volatile and non-volatile data memories for storing also of digital measuring or operating data internally ascertained and/or externally transmitted to the particular in line measuring device, and required for the safe performance of the bottling process —, in given cases, also for a retentive logging of the same —, data such as, for instance, chemical and/or physical properties of the medium to be measured, relevant for control of the bottling process and/or for the actual measuring. Besides the microcomputer and the driver circuit enabling the operating of the measuring transducer, the measuring device electronics additionally includes usually, for implementing the conditioning of the measurement signals delivered by the measuring transducer to the microcomputer, an input circuit, which is connected together with the microcomputer to form a measuring and evaluating circuit of the measuring device electronics. Based on the measurement signals delivered by the measuring transducer and/or on driver signals delivered from the measuring device electronics for driving the measuring transducer, the microcomputer ascertains, for the control of the bottling process, required primary measured values, such as, for instance, an instantaneous mass flow rate of the medium flowing through the measuring transducer and/or an integrated mass flow rate, which corresponds to a mass of the medium, which, during a predetermined period of time, especially a period of time corresponding with a predetermined amount of filling of the medium, such as, for instance, a filling period extending from an operating point in time corresponding to a starting point in time of an individual filling procedure up to an operating point in time corresponding to an end point in time of the same filling procedure, has totally flowed through the measuring transducer, and makes this available in real time.
Since conventional in line measuring devices of the type being discussed usually are embodied as independent measuring devices, which are to be integrated into a superordinated electronic data processing system controlling, for example, one or a number of filling machines and/or formed by means of programmable logic controllers (PLCs), especially via 2-wire or via 4-wire cable and/or wirelessly via radio, the particular measuring device electronics of a modern in line measuring device of the type being discussed includes most often also a corresponding communication circuit enabling the sending, or receiving, of measuring and/or operating data, for example, a communication circuit in the form of a digital output established in industrial measuring and automation technology, or in the form of an established 4-20-mA electrical current signal output, or in the form of a measurement transmitter interface meeting NAMUR recommendation NE43:1994 and/or PROFIBUS standard IEC 61158 or in the form of an interface circuit conforming to some other industrial standard. Moreover, provided in the measuring device electronics also is a supply circuit assuring the internal supplying of the in line measuring device with electrical energy, for example, drawing the energy from the electronic data processing system via 2-wire or via 4-wire cable and/or drawing the energy from an internal energy storer. Additionally, it is, such as, for example, mentioned in DE A 10 2006 013826, also usual directly to connect in line measuring devices of the type being discussed to the filling process controlling actuators, such as, for instance, valves and/or electric motors, in order to operate these essentially realtime with control commands, which are derived from the ascertained, totaled, mass flow as well as from therefor corresponding, predetermined, desired values.
In the case of the application of flow measuring, in line measuring devices having a measuring transducer of vibration-type, especially Coriolis mass flow measuring devices, in filling processes, it has, however, been found, that the accuracy of measurement, with which the respective primary measured values, especially the mass flow rate or the usually therefrom derived, integrated mass flow, are, in each case, ascertained, at flow conditions lying within predetermined specifications and even in the case of sufficiently known or also media properties held largely constant, such as, for instance, a density and a viscosity of the medium, can be subject to quite considerable fluctuations; this, especially, also, in spite of corresponding taking into consideration, for example, through targeted suppressing and/or corresponding compensating of the —, among others, discussed in the initially mentioned U.S. Pat. Nos. 7,296,484, 7,181,982, 7,040,181, 7,040,180, 6,910,366, 6,880,410, 6,471,487, 6,505,519, 6,311,136, 7,412,903, B 7,360,453, 7,360,452, US A 2008/0011101, US A 20080190195, WO A 06/127527, WO A 06/104690, WO A 05/093381, WO A 05/003690 or WO A 08/011587—circumstance, that the medium to be measured can, for process reasons, be formed of two or more phases, for example, as with liquid containing gas and/or solid, and/or, in spite of corresponding correction, in given cases, of known effects associated therewith on the respective measurement signals, such as, for instance, the so-called “bubble effect”, or the so-called “moving resonator effect”, etc. As a result of this, the accuracy of measurement can —, in spite of significant compensation, or eliminating, of known disturbing influences—lie possibly also far outside of a tolerance range acceptable for such filling or metering applications, even after taking into consideration the aforementioned disturbing influences. Especially, it has been found, first, that these disturbances caused by inhomogeneities in the medium, such as, for instance, gas bubbles and/or solid particles entrained in a liquid, have not only frequency equal to the oscillations of the measuring tube, but also each of the two sensor signals are burdened with an additional phase shift, and, indeed, in a manner changing the phase difference between the two sensor signals and, thus, also the phase difference between, in each case, one of the sensors, or also oscillation measurement signals, and the at least one exciter signal. As a result of this, the mass flow rate, m′, ascertained during different measuring cycles can assume, for instance, the curve shown dashed in FIG. 1a and the totaled mass flow, M′, ascertained during the same measuring cycles, for example, by integrating the mass flow rates measured one after the other, for instance, as shown by the likewise dashed curve in FIG. 1b. In comparison therewith, FIGS. 1a, 1b show the curves as a function of time for the actually set mass flow rate, m, and the actually flowed, totaled mass flow, M.
In additional tests, first, the recognized disturbing influence of the aforementioned inhomogeneities on the accuracy of measurement of the affected in line measuring devices was largely eliminated with the help of measures known from the state of the art, for example, by reducing the possibility of gas inclusions in the medium and/or by supplying the medium in the measuring transducer with a comparatively high pressure. Although, in such case, additionally, also, the stationary asymmetries in the flow profile, as discussed in the initially mentioned U.S. Pat. No. 6,513,393, brought about, for example, by pronounced curvatures of the measuring tubes and/or by turbulence in the flowing medium could largely be excluded, still, from time to time, after as before, considerable deviation of the so ascertained, primary measured values of the actual measured variables could be observed—this, especially, in the case of viscous, or thick, liquid, structurally viscous, thixotropic or pasty media, such as, for instance, syrup, honey, mayonnaise, yogurt, tomato paste, mustard, liquid detergents, glycerin or the like.
Further investigations under laboratory conditions using in line measuring devices of the type being discussed have, first of all, shown, that also for the case, in which the fraction of inhomogeneities in the medium relative to the, for the measuring, effective total volume of the at least one measuring tube is kept very small and constant, in spite of application of the corrective measures established for such filling processes, or for multiphase media, considerable inaccuracies in the primary measured variables, such as, for instance, primary measured values representing mass flow rate or totaled mass flow, can occur. Surprisingly, it has been found, in such case, even, that the measuring errors in the case of low concentration of inhomogeneities and/or in the case of low flow velocity can, at times, be larger, than in the case of a comparatively higher concentration, or in the case of higher flow velocities. Furthermore, it could be detected, that the measuring errors, counter to established operational experience, also in the case of an essentially perpendicularly installed measuring transducer with longitudinal axis extending in the direction of gravitation can, at times, be larger, than in the case of a horizontally installed measuring transducer. Additionally, in experiments with stepwise changed flow velocity of the medium and stepwise varied duration of the measuring cycles, it was observed, that, especially also in the case of totaled mass flow conventionally derived from the mass flow rate, considerable deviations from the actually flowed through mass-flow can, at times, occur in, first of all, non-reproducible manner, —this, especially, also in the case of mass flow rate held largely constant and largely uniformly low impurities loading of the medium—here, air bubbles in water (FIG. 1b).
Accordingly, it is to be assumed therefrom, that even only sometimes occurring inhomogeneities in the medium can also so directly affect the phase difference essential for the mass flow measurement, that the zero-point of the in line measuring device can, during operation, vary sporadically in considerable measure and in a manner not correctable with conventional corrective measures. As a result of this, conventional in line measuring devices of the type being discussed can, at times, exhibit a considerably lessened accuracy of measurement, or a lessened reproducibility, of the primary measured values, especially also in the case of the totaled mass flow eminently important for the control of filling processes. As a result of this, in the case of conventional in line measuring devices, in the case of an, for these, unfavorable loading of the medium with impurities and/or in the case of an unfavorable clocking of therewith controlled filling processes, a possible over—, or, such as in FIG. 1b, a corresponding underfilling, cannot always be excluded with certainty.